灰霾天气中硫的多元稳定同位素组成及其大气化学行为

With the aggravation of industrialization process, haze days appear frequently. Sulfur, as a key element,its atmospheric chemical behaviors have direct effects on the compositions of city haze aerosols, which result in a significant environmental effect. However, the relative studies are seldom conducted. Therefore, the project is to trace atmospheric chemical behaviors of sulfur based on multiple sulfur stable isotopic compositions (δ32S, δ33S, δ34S and δ36S) in haze aerosols from Nanjing regions. Specifically, we aim to clarify the main sulfur sources as well as transportation and transformation in the atmosphere during haze days, to retrieve photochemical reactions of SO2 in the stratosphere according to mass-independent sulfur isotopic fractionations (MIF-S) effect, and to explore the response of MIF-S effect with stratospheric O3 input to lower troposphere. In addition, this project is also to reveal the formation mechanisms of MIF-S effect in aerosols on the basis of simulated experiments, which can solve an international argument about whether photochemical reaction is a single source of anomalous fractionations for sulfur stable isotopes. The studies are favorable for unraveling atmospheric sulfur cycles as well as its environmental effect, and enriching fractionation theory of sulfur stable isotopes.

随着工业化进程的加剧，灰霾天气频繁出现。作为关键性元素，硫的大气化学行为直接影响城市灰霾气溶胶的组成，环境效应明显，但当前对其研究匮乏。本项目拟以南京地区为背景，系统研究灰霾气溶胶中硫的多元稳定同位素组成(δ32S、δ33S、δ34S与δ36S)，及其大气化学行为，明确灰霾天气下大气中硫的主要来源及其迁移转化规律。深入探讨灰霾气溶胶中硫稳定同位素的非质量分馏(MIF-S)效应，反演平流层SO2的光化学反应，洞察MIF-S效应对平流层O3入侵低空对流层的响应。通过模拟实验研究，揭示气溶胶颗粒中MIF-S效应的微观形成机制，解决光化学反应是否为MIF-S来源的唯一途径这一国际争论。研究可为阐明灰霾天气中硫的大气循环及其环境效应、丰富硫稳定同位素的分馏理论提供科学依据。

随着工业化进程的加剧，灰霾天气频繁出现，作为关键性元素，硫的大气化学行为直接影响城市灰霾气溶胶的组成，环境效应明显，本项目使用MAT-253同位素质谱仪对北京大气气溶胶中多硫同位素（32S、33S、34S与36S）和氧同位素（16O与18O）组成特征进行分析。结果显示，北京大气气溶胶中δ34S变化范围为1.68‰~12.57‰，平均值为5.86‰，表明该地区主要硫源与燃煤排放相关；δ18O变化范围为-5.29‰~9.02‰，平均值为5.17‰，说明气溶胶中的硫酸盐以二次硫酸盐为主。在2008年7月和8月，大气SO2主要以酸性条件下H2O2的异相氧化为主，而在9月和10月，大气SO2同时存在酸性条件下H2O2异相氧化和过量O2下Fe3+催化氧化。北京大气气溶胶存在显著的硫同位素非质量分馏（MIF-S）效应，通过对Δ33S与CAPE相关性分析，发现其形成机制不仅与平流层SO2的光化学反应有关，还可能与热化学反应机制关联，同时，Δ33S与O3呈显著正相关，说明O3入侵低空对流层可产生明显的MIF-S效应。同时依托硫同位素研究，扩展研究了南京地区四季大气气溶胶碳稳定同位素组成，冬、春、夏、秋四季南京市区PM2.1中δ13C均值分别为-24.42‰±1.12‰、-25.19‰±1.92‰、-25.79‰±0.45‰与-25.58‰±0.65‰，郊区分别为-25.34‰±1.18‰、-25.55‰±1.50‰、-25.31‰±0.55‰与-25.38‰±0.82‰。相关性分析和潜在污染源δ13C值表明，市区气溶胶PM2.1中碳质主要源于汽油车尾气排放，郊区工业区含碳物质源于尾气及工业排放，此外，燃煤源、生物质燃烧源及地质源等对两地冬春季气溶胶中碳质有重要贡献。